Did some googling and it appears that a cropping tag is applied to the RAW file when shooting in 1:1. Although the cropped data is still part of the RAW file, it may not be retrievable in LR, but is retrievable in DPP. In other words, with LR, you may be locked into 1:1, even with RAWs, while with DPP you can always restore the edges and revert back to 3:2. Go figure.